194 



Heredity and Environment 





Fig. 71. Normal and Inverse Symmetry of the 3D, 4th, 5TH and 6th 

 Cleavages. The cells la-id, 2a-2d and 2>a-2,d give rise to all the ectoderm; 

 6,d or M gives rise to mesoderm ; A, B, C, D to endoderm. 



and most fundamental differentiations which distinguished the 

 eggs of various phyla are not dependent upon the entering sperma- 

 tozoon. 



Share of Egg and Sperm in Heredity. — All of these corre- 

 spondences between the polarity, symmetry and pattern of the 



